Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

How 'Secondary' Sex Characters Can Drive the Origin of Species

27.08.2008
The ostentatious, sometimes bizarre qualities that improve a creature's chances of finding a mate may also drive the reproductive separation of populations and the evolution of new species, say two Indiana University Bloomington biologists.

In the September 2008 issue of Evolution (now online), Armin Moczek and Harald Parzer examine males from four geographically separated populations of the horned beetle species Onthophagus taurus. The beetles have diverged significantly in the size of the male copulatory organ, and natural selection operating on the other end of the animal -- horns atop the beetles' heads -- seems to be driving it.

"Biologists have known that in these beetles there is an investment trade-off between secondary sexual characters and primary sexual characters," Moczek said. "As horns get bigger, copulatory organs get smaller, or vice versa. What was not known was how frequently and how fast this can occur in nature, and whether this can drive the evolution of new species."

Structures directly involved in mating are known as primary sexual characters, whereas combat structures like horns -- or seductive attributes like a cardinal's vibrant plumage or a bullfrog's deeply resonant baritone -- are known as secondary sexual characters.

Evolutionary biologists believe changes in copulatory organ size and shape can spur speciation by making individuals from different populations sexually incompatible.

Native to Italy, O. taurus exists in other parts of the world only because of recent human activity. This means, Moczek and Parzer say, that the marked divergences they observed in O. taurus's horn and copulatory organ size must have occurred over an extremely short period of time -- 50 years or less.

Despite what many of us are led to believe, variation in male copulatory organ size within species tends to be very low, humans and beetles included. Yet the four O. taurus populations Moczek and Parzer studied in the U.S. (North Carolina), Italy, and western and eastern Australia, exhibit substantial changes in both horn and genitalia length -- as much as 3.5 times, in terms of an "investment" index the scientists devised that takes body size into account.

The scientists examined 10 other Onthophagus species, and as expected, they found vast differences between the species regarding horn and male copulatory organ size. Moczek says this suggests that trade-offs between primary and secondary sexual traits continue to shape the way species diverge well after speciation has occurred.

The speed and magnitude of divergence within O. taurus presents something of a paradox. How is it that copulatory organ size can be so rigorously maintained within the populations of a single species, yet appear so restless to change?

"In terms of the integrity of a species, it's important for these things not to change too much," Moczek explains. "So there is a lot of evidence suggesting that within species or within the populations of species, natural selection maintains genital characters. But if these primary sex characters are linked to other characters that can change readily, then you've got what we think is a very exciting mechanism that could prime populations for reproductive isolation."

Horn length and shape can change for many reasons, Moczek says. Among densely populated species, fighting (which favors large horns) may not be an effective strategy for winning mates. As combative males fight each other, a diminutive, smaller-horned male could simply employ a sneaking strategy to gain access to unguarded females. Under these circumstances, reduced investment in horns seems to result in larger copulatory organs. Alternately, in lower density populations, most male beetles spend a great deal of time fighting. Longer, bigger horns could serve these males well -- and also lead to smaller genitalia.

"If this is all it takes to change genitalia, it may be easier to make new species than we thought," Moczek said.

The notion that genital size is related to the origin of species is not new. But how they are related has perplexed evolutionary biologists. The individuals of most species do not choose mates according to the size and shape of genitalia. Indeed, genitalia may not be relevant until the latter stages of courtship, if at all.

An early "lock and key" model of reproductive isolation was first proposed by L. Dufour in 1844 to explain why some pairs of species, outwardly identical in every way, are unable to mate.

Research discussed in the Evolution paper was supported by grants from the National Science Foundation.

David Bricker | Newswise Science News
Further information:
http://www.indiana.edu

More articles from Life Sciences:

nachricht Nanoparticle Exposure Can Awaken Dormant Viruses in the Lungs
16.01.2017 | Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt

nachricht Cholera bacteria infect more effectively with a simple twist of shape
13.01.2017 | Princeton University

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

Im Focus: Bacterial Pac Man molecule snaps at sugar

Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.

The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...

Im Focus: Newly proposed reference datasets improve weather satellite data quality

UMD, NOAA collaboration demonstrates suitability of in-orbit datasets for weather satellite calibration

"Traffic and weather, together on the hour!" blasts your local radio station, while your smartphone knows the weather halfway across the world. A network of...

Im Focus: Repairing defects in fiber-reinforced plastics more efficiently

Fiber-reinforced plastics (FRP) are frequently used in the aeronautic and automobile industry. However, the repair of workpieces made of these composite materials is often less profitable than exchanging the part. In order to increase the lifetime of FRP parts and to make them more eco-efficient, the Laser Zentrum Hannover e.V. (LZH) and the Apodius GmbH want to combine a new measuring device for fiber layer orientation with an innovative laser-based repair process.

Defects in FRP pieces may be production or operation-related. Whether or not repair is cost-effective depends on the geometry of the defective area, the tools...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

Solar Collectors from Ultra-High Performance Concrete Combine Energy Efficiency and Aesthetics

16.01.2017 | Trade Fair News

3D scans for the automotive industry

16.01.2017 | Automotive Engineering

Nanoparticle Exposure Can Awaken Dormant Viruses in the Lungs

16.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>